1. Field of the Invention
The invention relates in general to electrical inductive apparatus, such as instrument transformers, and more specifically to new and improved high voltage current transformers.
2. Description of the Prior Art
Current transformers for high voltage application are frequently arranged in what are referred to as post-type enclosures. The enclosure includes a grounded tank portion and an insulating portion, for example, porcelain, which is quite tall and narrow to provide the necessary isolation from ground. Within this post-type enclosure is arranged a U-shaped or hair-pin primary winding or conductor for carrying current between terminals provided at the top of the enclosure which connect the hair-pin primary winding in the high voltage line. A secondary winding is provided around a length of the hair-pin primary winding at the lower end of the enclosure at low tension which may be used for measurement purposes. Substantial insulation is provided between the hair-pin primary winding and the secondary winding and between the hair-pin primary winding and the grounded portion of the enclosure. The enclosure is filled with oil which serves to improve the insulation and also provides for dissipation of heat generated in the conductors due both to r.sup.2 r loss and circulating currents. The only exit for the heat generated in the windings is through the oil and to the enclosure and from the enclosure to the surrounding air. Because of the shape of the current transformer structure, the heavy insulation and the shape of the primary winding, the circulation of the oil or other filling fluid is considerably hampered. As a result, it is difficult to properly cool the windings, in particular, the primary winding.